1. Field of the Invention
The present invention relates to photo lithography simulation techniques for predicting projected images precisely and in particular to a simulator of a lithography tool, a simulation method, and a computer program product for the simulator.
2. Description of the Related Art
As the semiconductor industry moves into a deep submicron range, costs associated with wafer processing are increasing rapidly. Therefore, repeating the wafer processing for optimizing processing conditions does not comply with a manufacturing cost. Hence, a lithography simulation that provides information for optimizing the wafer processing is required, However, identifying all parameters of an actual environment for lithography simulation is difficult. Japanese Patent Laid Open Publication No. Hei8-148404 discloses a simulation method modeling an exposure environment. But, it is still difficult to match the lithography simulation to actually obtained profiles even though the exposure environment is modeled. Accuracy of the lithography simulation is not sufficient, especially in a focus direction of a projection system. Recently, the numerical aperture (NA) of the projection system is increased to shrink the size of a semiconductor device. However, the higher the NA, the narrower a depth of focus (DOF). Therefore, a lithography simulation provides accurate information in the focus direction has been requested.